import java.util.Scanner;

public class Main {
    public static int Fac(int n) {
        if(n==1){
            return 1;
        }else if(n==2){
            return 1;
        }else{
            int f3=0;
            int f1=1;
            int f2=1;
            for (int i = 3; i <=n ; i++) {
                f3=f1+f2;
                f1=f2;
                f2=f3;
            }
            return f3;
        }
    }
    public static void main(String[] args) {
        Scanner scanner =new Scanner(System.in);
        int num= scanner.nextInt();
        System.out.println(Fac(num));
    }
}